Ported loudspeakers have been used to reduce acoustic re-radiation associated with the loudspeaker cabinet designs. For example, FIG. 1 depicts a cross-sectional view of a conventional ported loudspeaker 100. The loudspeaker 100 is housed in a cabinet 110, which includes a front baffle 120. In the example of FIG. 1, two drivers 130 and 140 are mounted to the baffle 120, although such ported loudspeakers 100 can have more or fewer drivers. Consistent with conventional ported loudspeakers, the port 150 is located on the front baffle 120, and adjacent to the drivers 130 and 140. Ducts 160 extend some distance back into the interior of cabinet 110. Numerous variations on the shape and length of the ducts 160 have been used in the prior art. It is generally known that the port 150 converts the rearward radiation of the bass loudspeaker into useful forward low frequency energy propagation, while providing low frequency output extension. Ported, or so-called ‘bass-reflex’ loudspeakers, are in common usage for a great many applications.
It is generally known that when the loudspeaker moves inward, it compresses the air within the cabinet, which in turn drives the “lump” of air outward through the duct. Its momentum takes it outside the body of the port a small distance, which rarifies the air inside the port, which then sucks the ‘lump’ of air back in.
While this activity is taking place, the loudspeaker is continuing its reciprocal movement, subsequently creating a partial vacuum and expanding the air within the cabinet. This decrease in pressure at the port inlet sucks the air in the port inward and the momentum of the air mass takes it beyond the port which compresses the air within the cabinet, which then drives the air mass back into the port, and so on.
This port radiation can be analogized to a vibrating mass connected to a spring, wherein the air within the port is a mass, the air within the cabinet functions as a spring and the driving force is the loudspeaker. At the resonant frequency of the port (i.e., the air mass within), small movements of the loudspeaker are needed to provide the power to keep the oscillation going.
Such ports have heretofore been mounted on the baffle of the loudspeaker, primarily so that all radiating sources are located beneath the grill covering. While ported loudspeakers may enjoy certain acoustical advantages over non-ported loudspeakers, with high-performance loudspeakers the ports can require substantial surface area to perform properly, thus making the loudspeaker substantially larger than otherwise needed for a non-ported system.
Accordingly, there is a need for a loudspeaker design which includes the benefits of a bass-reflex design, but without substantially adding to the size of the loudspeaker housing.